Is Texture Paint While In Viewport Render Possible With Cycles?
No, render view in Cycles will not update as you paint, no fix for this.
I have spent a lot of time painting in blender, and in the newer post 2.8 builds I find that either Solid View or Material Preview are the best to paint in regardless of which renderer I have set up, and for preview of the paint I swap to the Shading workspace to see it or just set up a duplicate editor in a small view and set that one to render view.